WO2020096253A1 - Positive electrode active material for lithium rechargeable battery, manufacturing method therefor and lithium rechargeable battery comprising same - Google Patents

Abstract

Disclosed are a positive electrode active material for a lithium rechargeable battery, a manufacturing method therefor and a lithium rechargeable battery comprising same, the positive electrode active material for a lithium rechargeable battery enabling the improvement of battery performance by having various types of carbon mixed and applied as a positive electrode active material. The positive electrode active material for a lithium rechargeable battery comprises two or more types of active material complexes having sulfur impregnated in a carbon material, wherein the carbon material included in any one type of active material complex, among the two or more types of active material complexes, differs from the carbon material included in another type of active material complex in terms of any one or more of average particle size and shape.

Description

Anode active material for lithium secondary battery, manufacturing method thereof and lithium secondary battery comprising the same

This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0136482 filed on November 8, 2018 and Korean Patent Application No. 10-2019-0133909 filed on October 25, 2019. All content disclosed in the literature is incorporated as part of this specification.

The present invention relates to a positive electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same, and more specifically, a lithium secondary battery for improving the performance of a battery by mixing and applying various types of carbon as a positive electrode active material The present invention relates to a positive electrode active material, a manufacturing method thereof, and a lithium secondary battery including the same.

As interest in energy storage technology increases, the application fields of mobile phones, tablets, laptops and camcorders, and even electric vehicles (EVs) and hybrid electric vehicles (HEVs) are expanding. Research and development of chemical devices is gradually increasing. The electrochemical device is the area that is receiving the most attention in this aspect, and among them, the development of a lithium-based secondary battery such as a lithium-sulfur battery capable of charging and discharging has become a focus of attention, and recently, in developing such a battery, capacity In order to improve the density and specific energy, it has led to research and development on the design of new electrodes and cells.

Among these electrochemical devices, especially lithium secondary batteries, lithium-sulfur (Li-S) batteries have high energy density and are in the spotlight as next-generation secondary batteries that can replace lithium-ion batteries. In such a lithium-sulfur battery, a reduction reaction of sulfur and an oxidation reaction of lithium metal occur during discharge, wherein sulfur is a lithium polysulfide having a linear structure from S ₈ of a ring structure (Li ₂ S ₂ , Li ₂ S ₄ , Li ₂ S ₆ , Li ₂ S ₈ ), which is characterized in that the lithium-sulfur battery exhibits a stepwise discharge voltage until polysulfide (PS) is completely reduced to Li ₂ S.

The sulfur anode of the lithium-sulfur battery is non-conductive, and most of the cathode material is a mixture of sulfur contributing to the electrochemical reaction and a conductive carbon-based material, which is a carrier, and is used in this case. Depending on the material, it affects the reactivity of the sulfur, high rate characteristics and life characteristics. However, in the lithium-sulfur battery, the electrode structure changes as the final reaction product Li ₂ S increases in volume compared to S, and the polysulfide, an intermediate product, dissolves easily in the electrolyte and continuously melts during the discharge reaction, resulting in the positive electrode active material. The amount decreases. As a result, degeneration of the battery is accelerated, and the reactivity and life characteristics of the battery are inevitably reduced. In order to solve this, technologies for modifying the surface of carbon have been developed, but there are difficulties that require long and complicated processes such as heat treatment, or the degree of elution reduction of polysulfide is weak, so no specific solution has been found. . Therefore, there is a need for a sulfur carrier capable of optimizing factors such as shape, size, and conductivity that affect battery performance.

Accordingly, an object of the present invention is to provide a positive electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery including the same, which can improve the performance of a battery by mixing and applying a variety of carbons as a positive electrode active material.

In order to achieve the above object, the present invention includes two or more active material complexes in which sulfur is supported on a carbon material, and the carbon material included in any one of the active material complexes of the two or more active material complexes is incorporated into an active material complex of another species. It provides a positive electrode active material for a lithium secondary battery characterized in that any one or more of the average particle size and shape of the carbon material included.

In addition, the present invention, (a) by mixing and reacting each of two or more different carbon materials having different one or more of the average particle size and shape with sulfur to prepare two or more active material composites in which sulfur is supported on each of the carbon materials. step; And (b) provides a method for producing a positive electrode active material for a lithium secondary battery comprising the step of mixing the two or more active material composite prepared above.

In addition, the present invention, the positive electrode containing the positive electrode active material for the lithium secondary battery; Lithium-based negative electrode; An electrolyte interposed between the positive electrode and the negative electrode; And a separator; provides a lithium secondary battery comprising a.

According to the positive electrode active material for a lithium secondary battery according to the present invention, a method of manufacturing the same, and a lithium secondary battery including the same, there is an advantage of improving performance such as battery life characteristics by mixing and applying various types of carbons as a positive electrode active material.

1 is a graph comparing and comparing the life characteristics of a lithium-sulfur battery according to an embodiment of the present invention and a lithium-sulfur battery according to a comparative example.

2 is a graph comparing and comparing the charging profile of a lithium-sulfur battery according to an embodiment of the present invention and a lithium-sulfur battery according to a comparative example.

Hereinafter, the present invention will be described in detail.

The positive electrode active material for a lithium secondary battery according to the present invention includes two or more active material complexes in which sulfur is supported on a carbon material, and the carbon material included in any one of the two or more active material complexes in the active material complex of another species Characterized in that at least one of the average particle size and the shape of the carbon material included is different.

The present applicant uses a lithium secondary battery, particularly, a carbon material applied as a sulfur carrier of a lithium-sulfur battery, having two or more types having different particle sizes and shapes, so that the lithium carrier having the advantages of each carbon material mixed is lithium secondary. It was applied to the battery to improve the life characteristics.

The active material composite is sulfur is supported on a carbon material, that is, as containing sulfur and carbon material, it can be used without limitation of two or more. For example, when the active material complex is two types, the first active material complex in which sulfur is supported on the first carbon material and the second active material complex in which sulfur is supported on the second carbon material are included, and the active material complex is three or more types In addition to the first and second active material complex, a third active material complex and the like may be further included. That is, in the present invention, the number of the active material composites, there is no particular limitation as long as the average particle size and shape of the carbon material contained in each active material composite are different from each other.

These active material composites may be mixed in various proportions as a positive electrode active material of a lithium secondary battery. For example, when two types of active material complexes are used, the mixing ratio may be 1: 9 to 9: 1 as a weight ratio, and preferably 2: 8 to 8: 2. In addition, when three or more types of active material complexes are used, they can be applied at an appropriate mixing ratio within a range not departing from the spirit of the present invention.

The carbon material included in each of the active material composites is for improving conductivity, and pores are provided to support sulfur, such as carbon nanotube (CNT), graphene and graphene oxide (GO). If it is formed and has a conductive carbon material, it can be used without particular limitation.

As described above, each carbon material included in each active material composite must achieve at least one of an average particle size and a shape different from each other to achieve the object of the present invention, which is to improve the life characteristics of a lithium secondary battery. The average particle size of the carbon material is 2 to 200 μm, preferably 5 to 100 μm, and if the average particle size of the carbon material is outside the above range, electrode coating failure may occur or slurry clogging may occur. If the particle sizes of the carbon materials included in the active material composite are not different from each other, the effect of improving the life characteristics of the battery may be very insignificant or not.

That is, for example, when the positive electrode active material includes two active material complexes, among the two active material complexes, the carbon material included in any one active material complex has an average particle size of 5 to 40 μm, and the other The carbon material included in the active material composite of the species may have an average particle size of 15 to 90 μm. As another example, when the positive electrode active material includes two active material complexes, among the two active material complexes, the carbon material included in any one active material complex has an average particle size of 5 μm or more and less than 25 μm, and other The carbon material included in one type of active material composite may have an average particle size of 25 μm or more to 90 μm or less.

Additionally, when the positive electrode active material includes two active material complexes, among the two active material complexes, the average particle size of the carbon material contained in one active material complex and the carbon contained in the other active material complex The average particle size difference of the material may be 5 to 65 μm, preferably 15 to 45 μm, and more preferably 25 to 35 μm. If the difference in average particle size of both carbon materials is less than 5 μm, there may be difficulty in maximizing the advantage due to the difference in average particle size, and when it exceeds 65 μm, there may be no more substantial benefit.

In addition, when the positive electrode active material includes two active material complexes, among the two active material complexes, the carbon material contained in any one active material complex having a relatively high average particle size and the other relatively small average particle size are different. The proportion of the carbon material contained in the active material composite of the species may be 1: 1 to 4: 1, preferably 2: 1 to 4: 1 as a weight ratio.

In the case of the carbon material shape, for example, if one is applied as a carbon nanotube, and the other is applied as another carbon material such as graphene oxide, the shape of each carbon material may naturally be different. On the other hand, if the same type of carbon material is used and the particle size is the same, the shape between the carbon materials must be different to improve the life characteristics of the battery. Here, when describing the shape of the carbon nanotube (CNT) among the carbon materials, the shape of the CNT is typically an entangle type in which the CNT is entangled to form a spherical shape, and the CNT is aligned and elongated in a certain direction. It can be classified as a bundle type that forms a skein of shape. The entangle type has an advantage in terms of overvoltage improvement or capacity development, and includes particles having an aspect ratio of 1 to 2. In addition, in the case of the bundle type, it is effective in improving high-rate properties and decomposing reaction by-products, and includes particles having an aspect ratio greater than 2. Therefore, it is preferable to configure the shape of each carbon material included in each active material composite differently to have all of these advantages.

In summary, each of the carbon materials included in each of the active material composites is different from each other (in this case, the average particle size and shape naturally vary), or in the case of the same type, any one or more of the average particle size and shape between the carbon materials Only if it is different can it meet the spirit of the present invention. Meanwhile, pores on which sulfur is supported are formed on the surface of the carbon material, and in this case, the pore volume of the carbon material may be 0.5 to 5 cm ³ .

Next, a method of manufacturing a positive electrode active material for a lithium secondary battery according to the present invention will be described. The method of manufacturing the positive electrode active material for a lithium secondary battery, (a) by mixing and reacting each of two or more different carbon materials having at least one of the average particle size and shape with sulfur, to which two or more types of sulfur supported on each of the carbon materials It includes a step of preparing an active material complex and (b) mixing the two or more active material complexes prepared above.

In the step (a), the active material composite may include two or more carbon materials having at least one of average particle size and shape, respectively. For example, when two types of active material composites are produced, the first active material composite is prepared by mixing and reacting sulfur and the first carbon material, and then, the second active material is mixed and reacted with sulfur and the second carbon material. There is no particular limitation on the number of active material complexes or the production order, such as the production of complexes and the production of each active material complex at the same time depending on the process environment, etc. (however, the number of active material complexes being manufactured must be two or more) . At this time, there is no particular limitation on the mixing ratio of sulfur and carbon materials contained in each active material composite.

In the step (a), the reaction may be carried out for 5 to 60 minutes, preferably 20 to 40 minutes at a temperature of 120 to 200 ° C, preferably 150 to 180 ° C. In addition, the definition of the carbon material, the description of the average particle size and shape, etc., is replaced by the above-described bar.

In the step (b), the prepared active material composites may be mixed in various ratios as a positive electrode active material of a lithium secondary battery. For example, when two types of active material complexes are used, the mixing ratio may be 1: 9 to 9: 1 as a weight ratio, and preferably 2: 8 to 8: 2. In addition, when three or more types of active material complexes are used, they can be applied at an appropriate mixing ratio within a range not departing from the spirit of the present invention. On the other hand, the active material complexes mixed in the step (b) are preferably in the form of a slurry, but there is no particular limitation on the mixed form unless it is outside the scope of the present invention, and it can be applied to those commonly used in the art.

Finally, when describing a lithium secondary battery including the positive electrode active material for a lithium secondary battery, the lithium secondary battery includes: a positive electrode comprising a positive electrode active material for a lithium secondary battery; Lithium-based negative electrode; An electrolyte interposed between the positive electrode and the negative electrode; And a separation membrane.

Here, the content of the positive electrode active material may be 50 to 95 parts by weight, preferably 60 to 90 parts by weight based on 100 parts by weight of the positive electrode. If the content of the positive electrode active material is less than 50 parts by weight relative to 100 parts by weight of the total positive electrode, the electrochemical properties of the battery due to the positive electrode active material may be lowered, and if it exceeds 95 parts by weight, a small amount of additional components such as binders and conductive materials As it may be included, it may be difficult to manufacture an efficient battery. In addition, the lithium secondary battery according to the present invention may be a lithium-based secondary battery such as a lithium-sulfur battery, a lithium metal battery, and a lithium air battery, but the lithium-sulfur battery may best meet the spirit of the present invention.

On the other hand, the overall configuration of the positive electrode, except for the positive electrode active material, the negative electrode, the electrolyte, and the separator may be a common one used in the art, and will be described below in detail.

The positive electrode included in the lithium secondary battery of the present invention further includes a binder and a conductive material in addition to the positive electrode active material described above. The binder is a component that assists in the bonding of the positive electrode active material and the conductive material and the like to the current collector, for example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF / HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl (meth) acrylate, polyethyl (meth) acrylate, polytetrafluoroethylene (PTFE) ), Polyvinylchloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene -Butylene rubber, fluorine rubber, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, and One or more kinds selected from the group consisting of these mixtures may be used, but is not limited thereto.

The binder is usually 1 to 50 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the total positive electrode. If the content of the binder is less than 1 part by weight, the adhesive force between the positive electrode active material and the current collector may be insufficient, and if it exceeds 50 parts by weight, the adhesive strength is improved, but the content of the positive electrode active material decreases, so that the battery capacity may be lowered.

The conductive material included in the positive electrode is not particularly limited as long as it has excellent electrical conductivity without causing a side reaction in the internal environment of the lithium secondary battery and does not cause a chemical change in the battery, and typically graphite or conductive carbon can be used. Graphite, such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, furnace black, lamp black, and summer black; A carbon-based material having a crystal structure of graphene or graphite; Conductive fibers such as carbon fibers and metal fibers; Carbon fluoride; Metal powders such as aluminum and nickel powders; Conductive whiskey such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; And conductive polymers, such as polyphenylene derivatives; may be used alone or in combination of two or more, but is not limited thereto.

The conductive material is usually added in 0.5 to 50 parts by weight, preferably 1 to 30 parts by weight based on 100 parts by weight of the total weight of the positive electrode. If the content of the conductive material is less than 0.5 part by weight, it is difficult to expect an effect of improving the electrical conductivity or the electrochemical properties of the battery may be deteriorated. If the content of the conductive material exceeds 50 parts by weight, the amount of the positive electrode active material is relatively high. Less, the capacity and energy density may decrease. The method of including the conductive material in the positive electrode is not particularly limited, and a conventional method known in the art, such as coating on a positive electrode active material, can be used. In addition, if necessary, the addition of a conductive material as described above may be substituted because a conductive second coating layer is added to the positive electrode active material.

Further, a filler may be optionally added to the positive electrode of the present invention as a component that inhibits its expansion. The filler is not particularly limited as long as it can suppress the expansion of the electrode without causing a chemical change in the battery, and for example, olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fiber and carbon fiber; Etc. can be used.

The positive electrode of the present invention can be prepared by dispersing and mixing the positive electrode active material, binder, and conductive material in a dispersion medium (solvent) to form a slurry, and then applying it on a positive electrode current collector, followed by drying and rolling. As the dispersion medium, NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof may be used, but are not limited thereto.

The positive electrode current collector includes platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), aluminum (Al ), Molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ), and alloys thereof , Surface treatment of carbon (C), nickel (Ni), titanium (Ti) or silver (Ag) on the surface of aluminum (Al) or stainless steel may be used, but is not limited thereto. The positive electrode current collector may be in the form of foil, film, sheet, punched, porous body, foam, or the like.

The cathode may be manufactured according to a conventional method known in the art. For example, a negative electrode active material, a conductive material, a binder, and a filler, if necessary, can be dispersed and mixed in a dispersion medium (solvent) to make a slurry, and then coated on a negative electrode current collector, followed by drying and rolling to produce a negative electrode. . As the negative electrode active material, a lithium metal or a lithium alloy (eg, an alloy of lithium and a metal such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium) may be used. Examples of the negative electrode current collector include platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), and copper (Cu) ), Molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO ₂ ), FTO (F doped SnO ₂ ), and alloys thereof , Surface treatment of copper (Cu) or stainless steel with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag) may be used, but is not limited thereto. The shape of the negative electrode current collector may be in the form of foil, film, sheet, punched, porous body, foam, or the like.

The separator is interposed between the positive electrode and the negative electrode to prevent a short circuit between them and serves to provide a passage for lithium ions. As the separator, olefin-based polymers such as polyethylene and polypropylene, glass fibers, and the like can be used in the form of sheets, multi-layer membranes, microporous films, woven fabrics, and non-woven fabrics, but are not limited thereto. On the other hand, when a solid electrolyte such as a polymer (eg, organic solid electrolyte, inorganic solid electrolyte, etc.) is used as the electrolyte, the solid electrolyte may also serve as a separator. Specifically, an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator may generally range from 0.01 to 10 μm, and the thickness may generally range from 5 to 300 μm.

As the electrolyte or electrolyte, a carbonate, ester, ether, or ketone may be used alone or in combination of two or more as a non-aqueous electrolyte (non-aqueous organic solvent), but is not limited thereto. For example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butylolactone, n-methyl acetate, n- Such as ethyl acetate, n-propyl acetate, phosphoric acid triester, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran Tetrahydrofuran derivatives, dimethylsulfoxide, formamide, dimethylformamide, dioxolane and its derivatives, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3- Aprotic organic solvents such as dimethyl-2-imidazolidinone, methyl propionate, and ethyl propionate may be used, but are not limited thereto. It is not.

A lithium salt may be further added to the electrolyte solution (so-called non-aqueous electrolyte solution containing lithium salt), and the lithium salt is a well-known one that is soluble in a non-aqueous electrolyte solution, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiPF ₃ (CF ₂ CF ₃ ) ₃ , LiAlCl ₄ , CH ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lower aliphatic lithium carboxylate, lithium phenyl borate, lithium imide, and the like, but are not limited thereto. The (non-aqueous) electrolytic solution is for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, glyme-based compound, hexamethylphosphoric acid tria Addition of mid, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. It may be. If necessary, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included to impart non-flammability, or carbon dioxide gas may be further included to improve high temperature storage characteristics.

On the other hand, the lithium secondary battery of the present invention can be manufactured according to a conventional method in the art. For example, it can be produced by placing a porous separator between the positive electrode and the negative electrode, and adding a non-aqueous electrolyte. The lithium secondary battery according to the present invention is applied to a battery cell used as a power source for a small device, and can be particularly suitably used as a unit cell of a battery module that is a power source for a medium-to-large-sized device. In this aspect, the present invention also provides a battery module including two or more lithium secondary batteries are electrically connected (serial or parallel). Of course, the number of lithium secondary batteries included in the battery module may be variously adjusted in consideration of the use and capacity of the battery module.

Furthermore, the present invention provides a battery pack electrically connecting the battery modules according to conventional techniques in the art. The battery module and the battery pack are a power tool (Power Tool); An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), and a plug-in hybrid electric vehicle (PHEV); Electric truck; Electric commercial vehicles; Alternatively, the power storage system may be used as a power supply for any one or more medium and large devices, but is not limited thereto.

Hereinafter, preferred embodiments are provided to help the understanding of the present invention, but these are merely illustrative of the present invention, and it is apparent to those skilled in the art that various changes and modifications can be made within the scope and technical scope of the present invention. It is also natural that the modifications fall within the scope of the appended claims.

[Example 1] Preparation of positive electrode active material

First, a first active material composite was prepared by mixing sulfur and carbon nanotubes having an average particle size of 57.27 μm and an entangled shape in a weight ratio of 7.5: 2.5 and reacting at 155 ° C. for 30 minutes. Carbon nanotubes having a particle size of 22.59 µm and a bundle shape were mixed in a weight ratio of 7.5: 2.5 and then reacted at 155 ° C. for 30 minutes to prepare a second active material composite. Subsequently, the prepared first active material composite and the second active material composite were stirred and mixed at a rate of 1,500 rpm when preparing a slurry in a weight ratio of 8: 2, thereby preparing a positive electrode active material.

[Example 2] Preparation of positive electrode active material

A positive electrode active material was prepared in the same manner as in Example 1, except that the first active material composite and the second active material composite were mixed by changing to a weight ratio of 5: 5 instead of a weight ratio of 8: 2.

[Example 3] Preparation of positive electrode active material

A positive electrode active material was prepared in the same manner as in Example 1, except that the first active material composite and the second active material composite were mixed by changing to a weight ratio of 2: 8 instead of a weight ratio of 8: 2.

[Comparative Example 1] Preparation of positive electrode active material

A positive electrode active material was prepared by mixing sulfur and carbon nanotubes having an average particle size of 57.27 µm and having an entangled shape in a weight ratio of 7.5: 2.5 and reacting at 155 ° C. for 30 minutes (ie, in the first active material composite of Example 1). Applicable).

[Comparative Example 2] Preparation of positive electrode active material

A positive electrode active material was prepared by mixing carbon nanotubes having an average particle size of 22.59 μm and a bundle shape in a weight ratio of 7.5: 2.5 and reacting at 155 ° C. for 30 minutes (that is, in the second active material composite of Example 1). Applicable).

[Examples 4 to 6 and Comparative Examples 3 to 4] Preparation of lithium-sulfur batteries

Preparation of anode for lithium-sulfur batteries

The positive electrode active materials prepared in Examples 1 to 3 and Comparative Examples 1 and 2, super-P as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 88: 5: 7, and NMP solvent After preparing the slurry by dispersing it on, it was coated with a thickness of 500 μm on an aluminum current collector (Al foil), and then dried in a vacuum oven at 120 ° C. for 13 hours to prepare a positive electrode for a lithium-sulfur battery.

Preparation of lithium-sulfur batteries

After placing the prepared positive electrode to face the negative electrode (Li metal foil), a polyethylene separator was interposed therebetween, and then, a lithium-sulfur battery was injected by injecting an electrolyte solution in which LiFSI was dissolved at a concentration of 4 M in a dimethyl ether solvent. It was prepared.

[Experimental Example 1] Evaluation of battery life characteristics

The remaining capacity of the lithium-sulfur batteries prepared in Examples 4 to 6 and Comparative Examples 3 and 4 was repeated according to charge and discharge, and the life characteristics of each lithium-sulfur battery were evaluated. 1 is a graph comparing the life characteristics of a lithium-sulfur battery according to an embodiment of the present invention and a lithium-sulfur battery according to a comparative example, and FIG. 2 is a lithium-sulfur battery according to an embodiment of the present invention It is a graph comparing and comparing the charging profile of the lithium-sulfur battery according to the comparative example.

1 and 2, a lithium-sulfur battery (Examples 4 to 6) in which two or more active material complexes are applied as a positive electrode active material according to the present invention is usually applied to one single active material complex as a positive electrode active material. Compared with the lithium-sulfur batteries (Comparative Examples 3 and 4), it was confirmed that the life characteristics were improved. In particular, in the case of the battery prepared in Example 4, as can be seen through FIG. 2, it was found that the initial discharge capacity also increased compared to the batteries prepared in Comparative Examples 3 and 4. Through this, it can be seen that, as in the present invention, when various kinds of carbon materials are mixed in an appropriate ratio and applied as a sulfur carrier, the performance of the battery, such as life characteristics, becomes excellent.

Claims (14)

1. Sulfur contains a composite of two or more active materials supported on a carbon material,

   The positive electrode active material for a lithium secondary battery is characterized in that the carbon material contained in one of the active material composites of the two or more active material composites has at least one of an average particle size and shape different from that of the carbon material contained in the active material composite of another species.
2. The positive electrode active material for a lithium secondary battery according to claim 1, wherein the positive electrode active material includes two active material complexes, and the two active material complexes are contained in a weight ratio of 1: 9 to 9: 1.
3. The method according to claim 1, The average particle size of the carbon material is characterized in that 2 to 200 ㎛, the positive electrode active material for a lithium secondary battery.
4. The method according to claim 2, Of the two types of active material composite, the carbon material contained in one of the active material composite has an average particle size of 5 to 40 ㎛, the average particle size of the carbon material included in the other type of active material composite is 15 to 90 A positive electrode active material for a lithium secondary battery, characterized in that it is µm.
5. The method according to claim 2, Of the two kinds of active material composite, the carbon material contained in any one of the active material composite has an average particle size of 5 μm or more to less than 25 μm, and the carbon material included in the other type of active material composite has an average particle size. A positive electrode active material for a lithium secondary battery, characterized in that it is 25 μm or more to 90 μm or less.
6. The method according to claim 2, Of the two active material composites, the average particle size difference of the carbon material contained in one of the active material composites, the average particle size difference of the carbon material contained in the other active material composite is 5 to 65 ㎛ Characterized in that, the positive electrode active material for a lithium secondary battery.
7. The method according to claim 1, The carbon material is characterized in that is selected from the group consisting of carbon nanotubes, graphene and graphene oxide, a positive electrode active material for a lithium secondary battery.
8. The method according to claim 7, The carbon material is a carbon nanotube, the shape is characterized in that the entangle type or bundle type, the positive electrode active material for a lithium secondary battery.
9. The method according to claim 8, wherein the carbon nanotube of the entangle type includes particles having an aspect ratio of 1 to 2, and the bundle type carbon nanotube includes particles having an aspect ratio of more than 2. , Positive electrode active material for lithium secondary batteries.
10. (a) mixing and reacting each of two or more carbon materials having different one or more of average particle size and shape with sulfur to prepare two or more active material composites in which sulfur is supported on each of the carbon materials; And

    (B) a method of manufacturing a positive electrode active material for a lithium secondary battery comprising the step of mixing the composite of two or more of the prepared active materials.
11. The method according to claim 10, wherein the active material complex is one of two active material complexes included, and the two active material complexes are characterized in that they are mixed in a weight ratio of 1: 9 to 9: 1, producing a positive electrode active material for a lithium secondary battery. Way.
12. The method according to claim 10, The reaction is characterized in that is carried out for 5 to 60 minutes at a temperature of 120 to 200 ℃, the method for producing a positive electrode active material for a lithium secondary battery.
13. A positive electrode comprising a positive electrode active material for a lithium secondary battery of claim 1; Lithium-based negative electrode; An electrolyte interposed between the positive electrode and the negative electrode; And a separator; a lithium secondary battery.
14. The lithium secondary battery according to claim 13, wherein the lithium secondary battery is a lithium-sulfur battery.

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